Heat-exchanger

ABSTRACT

There is provided a heat-exchanger in which the heattransmitting surfaces are made of plastic and consist of at least one helically wound tube, which is arranged within an annular space. The tubes are formed with corrugations extending around the circumference of the tubes and are arranged in spirals one outside the other, the spirals being separated by longitudinal plastic strips which preferably have notches for the tubes.

United States Patent [191 Margen Nov. 26, 1974 [54] HEAT-EXCHANGER [75] Inventor: Peter Heinrich Erwin Margen,

. Nykoping, Sweden [73] Assignee: Aktiebolaget Atomenergi,

Stockholm, Sweden [22] Filed: Apr. 2, 1973 [21] Appl. No: 347,176

[30] Foreign Application Priority Data Apr. 6, 1972 Sweden 4470/72 [52] US. Cl 165/66, 165/140, 165/156 [51] Int. Cl. F28d 7/04, F28f 21/06, F28f 1/08 [58-] Field of Search 165/53, 66, 75, 132, 140,

[56] References Cited UNITED STATES PATENTS 7/1934 Hewitt et a1. 165/66 X 2,103,947 12/1937 Holmes 165/140 X 2,819,731 l/l958 Louthan 165/177 X 3,199,583 8/1965 Houd, Jr. et al..... 165/175 X 3,277,959 10/1966 Withers 165/180 X 3,306,352 2/1967 Curren 1. 165/163 Primary Examiner-Charles J. Myhre Assistant ExaminerTheophil W. Streule, Jr. Attorney, Agent, or FirmToren, McGeady and Stanger [5 7 ABSTRACT There is provided a heat-exchanger in which the heattransmitting surfaces are made of plastic and consist of at least one helically wound tube, which is arranged within an annular space. The tubes are formed with corrugations extending aroundlthe circumference of the tubes and are arranged in spirals one outside the other, the spirals being separated by longitudinal plastic strips which preferably have notches for the tubes.

5 Claims, 3 Drawing Figures HEAT-EXCHANGER The invention relates to a heat-exchanger in which the heat-transmitting surfaces are made of plastic. It is already known that plastic tubes can be used in heatexchangers. The heat-exchanger is then usually designed as a conventional tube heat-exchanger, i.e. the plastic tubes are straight and their ends are inserted in end pieces. However, this conventional method does not make full use of the advantages of plastic from a price point of view since the cost of tube plates and attachment of the tubes considerably exceeds the cost of the extremely cheap plastic tubes.

The invention aims to provide a construction which is suitable for plastic tubes, particularly thin-walled plastic tubes. One object of the invention is to produce a heat-exchanger which can be constructed without the use of special tools. Another object is to produce a heat-exchanger having a large heat-transmitting surface, which can be used to heat air by means of hot water, especially for heating dwellings. Other objects will appear in the following description.

The heat-exchanger according to the invention is characterized in that the heat-transmitting surfaces consist of at'least one plastic tube which has been helically wound. A preferred embodiment is characterized in that the helically wound plastic tube is arranged in an annular space limited by an inner cylindrical wall and an outer cylindrical wall and that the inlets and outlets for the heat-exchanging medium surrounding the plastic tube are arranged at the ends of the annular space so that the medium flows substantially perpendicular to the plastic tube. In this preferred embodiment, therefore, there is a space inside the inner cylindrical wall. In this space heat-transfer surfaces are suitably arranged to pre-heat the medium to be heated.

The plastic tube, or plastic tubes, is preferably corrugated, i.e. has alternating protuberances and depressions extending around the circumference of the tube. Such a corrugated tube is easy to bend to form a spiral, it offers a larger heat-transfer surface than a smooth tube and the corrugations give the tube added strength, thus making it possible to use thin-walled tubes. Further, the corrugations make it possible to use rigid plastic, for example stiff polyvinyl chloride as material for the tubes.

The invention will now be described with reference to the accompanying drawing.

FIG. 1 shows a longitudinal section through a heatexchanger according to the invention, intended for heating living accommodations.

FIG. 2 shows a section along the line AA in FIG. 1.

FIG. 3 shows on a larger scale a section along the line 8-8 in FIG. 1.

The illustrated heat-exchanger has two coaxial cylindrical walls, namely an inner wall 2 and an outer wall 3. At one end the cylindrical walls 2, 3 are joined to each other by means of an end wall 5. At the other end the cylindrical wall 3 is provided with an end wall 4 and the cylindrical wall 2 ends little way from the end wall 4 so that an annular gap 11 is formed here. In the annular space 14 thus formed between the walls 2 and 3, two helically wound plastic tubes la and 1b are arranged. The tube lb is supported by a plurality of longitudinal plastic strips 17b which are placed on the inner cylindrical wall 2. A plurality of longitudinal plastic strips 17a are placed on the tube 1b, and these support the outer, helically wound tube la. The plastic strips 17 are provided with notches 17c for the tubes, and thus act as spacers and support means for the tubes. The tubes are provided with corrugations running around the circumference, see FIG. 3.

At one end the tubes la, 1b extend through an inlet box 7 and are connected to a water-container 6, open to the atmosphere. Hot water is supplied to the container through a conduit 20 and the level in the container is kept constant by means of a valve 21, regulated by a float 22. At the other end the tubes la, lb pass through an outlet box 8 and are connected to a return water conduit 23.

In the space inside the inner cylindrical wall 2, a bundle of tubes 9a run longitudinally and these are also preferably corrugated in order to provide a large surface. At one end the tubes 9a are attached in an end piece 19b which is attached to the annular end wall 4. This end of the tubes 9a communicates with an inlet section 19a which is attached by a flange 190 to an outlet tube 12 for evacuation air from a building. The other end of the tubes 9a extends slightly outside the end wall 5 of the annular space 14 and is attached in an end piece 290 and communicates with an outlet part 29a which is attached by. a flange 29c to an exhaust tube 13 for the evacuation air. An annular inlet gap 30 is formed between the end wall 5 and the end piece 29b.

Close to the end wall 5 the annular space 14 communicates with an outlet part 15 which is attached by a flange 31 to an inlet channel 32 for heated fresh air for the building. A fan 16, driven by a motor 33, is arranged in the outlet part 15.

The heat-exchanger described above functions as follows, a few temperatures being introduced as examples.

Cold fresh air of 0C is sucked in through the inlet gap 30 and passes along the tubes 9a in counter current with the evacuation air flowing in the tubes 9a. The fresh air is pre-heated to 7C while the evacuation air is cooled from 20C to 13C. The preheated fresh air flows through the gap 11 and passes through the annular space 14 where it is warmed by the hot water in the tubes 1 to 20C. At this temperature the air is blown by the fan 16 to the various rooms of the building. Hot water is supplied to the tubes 1 at 40C and leaves the heat-exchanger at 20C.

The illustrated heat-exchanger is suitably made entirely of plastic and the various parts are attached to each other by means of glueing. The inexpensive plastic material and method of manufacture by glueing involves very little-cost. The uniformity of the material used avoids problems caused by different coefficients of thermal expansion, adhesion, etc.

The use of corrugated tubes provides the flexibility necessary to enable the tubes to be wound into spirals without any special tools, while at the same time offering an enlarged surface and increased turbulence for the heat-transfer. The helical shape induces countercurrent between water and air so that the hottest water encounters the hottest air, which is also an advantage for heat-transfer. The helical shape also means that the desired long flow path on the water side can be achieved, permitting acceptably high water speeds and relatively small and thus inexpensive tube plates and end pieces. Finally, the helical shape permits transverse air flow which increases turbulence and thus improves the heat transmission.

The coaxial combination of the walls 2, 3 and the tube bundle 9a, these parts being connected to each other only at one end, permits free expansion of all these parts and thus prevents temperature stresses due to temperature differences between these parts. The coaxial construction is also very compact and uses a minimum of material since, for example, the same wall 2 constitutes the inner wall of the main heat-exchanger and the outer wall of the pre-heater at the same time as the outlet opening 11 for the pre-heater constitutes the inlet opening for the main heat-exchanger.

The use of corrugated tubes for the pre-heater as well provides an increased heat-transfer surface and turbulence, which is particularly important here since the flow is parallel to the tubes.

The corrugations also give increased strength against internal (and external) over-pressure per unit of heattransmitting surface and given wall-thickness in comparison with smooth tubes, which is of importance, especially for the tubes 1.

The open tank 6 limits the over-pressure on the tubes 1.

The entire unit can easily be disconnected by disconnecting two water flanges and three air-pipe flanges, after which a faulty unit can be replaced by a reserve unit or a new unit while repairs are carried out.

What is claimed is:

l. A heat-exchanger comprising an axially elongated inner cylindrically shaped wall, an axially elongated outer cylindrically shaped wall laterally enclosing and spaced radially outwardly from said inner wall and forming an axially extending annular shaped flow space therebetween, first means associated with said inner and outer walls for closing the opposite ends of the annular space, said inner wall in cooperation with said first means arranged to fomr an inlet into said annular space located at one end thereof, second means in cooperation with said outer wall for forming an outlet from said annular space at the opposite end from said inlet, heat transmitting surfaces formed of plastic disposed within said annular space and comprising at least a first corrugated plastic tube and second corrugated plastic tube with the corrugations extending transvcrsely of the axial direction of said tubes, said first corrugated plastic tube helically wound about said inner wall within said annular space and extending in the axial direction through said annular space, said second corrugated plastic tube helically wound about and spaced radially outwardly from said helically wound first tube within said annular space and extending in the axial direction through said annular space, said second tube being spaced radially inwardly from said outer wall so that flow can pass in the axial direction through said annular space between said first and second tubes and between said second tube and the inner surface of said outer wall, plastic strips located within and extending in the axial direction of said annular space between said inner tube and said first tube and between said first and second tubes for supporting and spacing said first and second tubes, said plastic strips spaced apart in the circumferential direction of said inner wall to afford flow through said annular space to pass between and over the outer surfaces of said first and second tubes, third means for circulating hot water as a heat transfer medium through said first and second plastic tubes for passing the hot water in indirect heat transfer relationship with air flowing as a heat transfer medium over said tubes in axial flow from the inlet to the outlet of said annular space affording substantially perpendicular and countercurrent flow relationship to the helically wound coils of said inner and outer tubes.

2. A heat-exchanger comprising an axially elongated inner cylindrically shaped wall, an axially elongated outer cylindrically shaped wall laterally enclosing and spaced radially outwardly from said inner wall and forming an axially extending annular shaped flow space therebetween, first means associated with said inner and outer walls for closing the opposite ends of the an-' nular space, said inner wall in cooperation with said first means arranged to form an inlet at one end to said annular space, second means in cooperation with said outer wall arranged to form an outlet from said annular space at the opposite end thereof from said inlet, heat transmitting surfaces formed of plastic disposed withinsaid annular space and comprising at least a first corrugated plastic tube and a second corrugated plastic tube, said first corrugated plastic tube helically wound about said inner wall within said annular space and extending in the axial direction through said annular space, said second corrugated plastic tube helically wound about and spaced radially outwardly from said helically wound first tube within said annular space and extending in the axial direction through said annular space, said second tube being spaced radially inwardly from said outer wall so that flow can pass in the .axial direction through said annular space between siad first and second tubes and between said second tube and the inner surface of said outer wall, plastic strips located within said annular space and extending in the axial direction thereof for supporting and spacing said first and second tubes, said plastic strips spaced apart in the circumferential direction of said inner wall to afford flow through said annular space to pass between and over the outer surfaces of said first and second tubes, third means for circulating hot water as a first heat transfer medium through said first and second plastic tubes for passing the hot water in indirect heat transfer relationship with air flowing as a second heat transfer medium passing over said tubes in axial flow from the inlet to the outlet of said annular space in substantially perpendicular and countercurrent flow relationship to the helically wound coils of said inner and outer tubes, a plurality of spaced tubes extending axially to the space defined within said inner wall, means for passing a third heat transfer medium through said straight tubes, the space within said inner wall and surrounding the spaced tubes therein being open at one end to the atmosphere surrounding the heat-exchanger and being closed at its opposite end and the inlet to said annular space located at and being in communication with the opposite end of the space within said inner wall so that the second heat transfer medium, prior to flowing over said first and second plastic tubes, passes over said spaced tubes in the space within said inner wall so that the second heat transfer medium is preheated in advance of its introduction into said annular space.

3. A heat-exchanger, as set forth in claim 2, wherein said first means comprises a first annularly shaped end wall extending between said inner wall and said outer wall transversely of the axial direction thereof and forming a closure for one end of said annular space therebetween, and a second annularly shaped end wall connected to and extending radially inwardly from said outer wall transversely of the axial direction of said outer wall at the opposite end thereof from said first end wall and with the adjacent end of said inner wall spaced in the axial direction thereof from said second end wall toward said first end wall so that the space therebetween forms the inlet to said annular space, said second means comprises an outlet member connected to and extending outwardly from said outer wall adjacent said first end wall for forming the outlet from said annular space, said third means comprises a container located radially outwardly from said outer wall relative to said inner wall, an inlet box connected between said container and said outer wall, said first and second tubes extending through said inlet box and connected to said container for receiving hot water from said container for flow through said tubes, an outlet box connected to said outer wall at the opposite end thereof from said inlet box and arranged to receive the outlet ends of said first and second tubes, inlet means connected to said spaced tubes within said inner wall and spaced axially outwardly from said first end wall so that the space within said inner wall is opened at the end adjacent said inlet means, and outlet means connected to said spaced tubes within said inner wall and connected to said second end wall and extending transversely of the axial direction of said inner wall and fonning a closure for the end of said space within said inner wall opposite the end located adjacent said inlet means,

4. A heat-exchanger, as set forth in claim 3, wherein said inner wall and outer wall, said straight tubes, said inlet and outlet means for said tubes, and said container, said inlet box and outlet box associated with said helically wound first and second tubes are all formed of plastic material.

5. A heat-exchanger, as set forth in claim 3, wherein said container is open to the atmosphere, and a level regulator located within said container for regulating the level of hot water therein for limiting the pressure within said first and second tubes. 

1. A heat-exchanger comprising an axially elongated inner cylindrically shaped wall, an axially elongated outer cylindrically shaped wall laterally enclosing and spaced radially outwardly from said inner wall and forming an axially extending annular shaped flow space therebetween, first means associated with said inner and outer walls for closing the opposite ends of the annular space, said inner wall in cooperation with said first means arranged to form an inlet into said annular space located at one end thereof, second means in cooperation with said outer wall for forming an outlet from said annular space at the opposite end from said inlet, heat transmitting surfaces formed of plastic disposed within said annular space and comprising at least a first corrugated plastic tube and second corrugated plastic tube with the corrugations extending transversely of the axial direction of said tubes, said first corrugated plastic tube helically wound about said inner wall within said annular space and extending in the axial direction through said annular space, said second corrugated plastic tube helically wound about and spaced radially outwardly from said helically wound first tube within said annular space and extending in the axial direction through said annular space, said second tube being spaced radially inwardly from said outer wall so that flow can pass in the axial direction through said annular space between said first and second tubes and between said second tube and the inner surface of said outer wall, plastic strips located within and extending in the axial direction of said annular space between said inner tube and said first tube and between said first and second tubes for supporting and spacing said first and second tubes, said plastic strips spaced apart in the circumferential direction of said inner wall to afford flow through said annular space to pass between and over the outer surfaces of said first and second tubes, third means for circulating hot water as a heat transfer medium through said first and second plastic tubes for passing the hot water in indirect heat transfer relationship with air flowing as a heat transfer medium over said tubes in axial flow from the inlet to the outlet of said annular space affording substantially perpendicular and countercurrent flow relationship to the helically wound coils of said inner and outer tubes.
 2. A heat-exchanger comprising an axially elongated inner cylindrically shaped wall, an axially elongated outEr cylindrically shaped wall laterally enclosing and spaced radially outwardly from said inner wall and forming an axially extending annular shaped flow space therebetween, first means associated with said inner and outer walls for closing the opposite ends of the annular space, said inner wall in cooperation with said first means arranged to form an inlet at one end to said annular space, second means in cooperation with said outer wall arranged to form an outlet from said annular space at the opposite end thereof from said inlet, heat transmitting surfaces formed of plastic disposed within said annular space and comprising at least a first corrugated plastic tube and a second corrugated plastic tube, said first corrugated plastic tube helically wound about said inner wall within said annular space and extending in the axial direction through said annular space, said second corrugated plastic tube helically wound about and spaced radially outwardly from said helically wound first tube within said annular space and extending in the axial direction through said annular space, said second tube being spaced radially inwardly from said outer wall so that flow can pass in the axial direction through said annular space between siad first and second tubes and between said second tube and the inner surface of said outer wall, plastic strips located within said annular space and extending in the axial direction thereof for supporting and spacing said first and second tubes, said plastic strips spaced apart in the circumferential direction of said inner wall to afford flow through said annular space to pass between and over the outer surfaces of said first and second tubes, third means for circulating hot water as a first heat transfer medium through said first and second plastic tubes for passing the hot water in indirect heat transfer relationship with air flowing as a second heat transfer medium passing over said tubes in axial flow from the inlet to the outlet of said annular space in substantially perpendicular and countercurrent flow relationship to the helically wound coils of said inner and outer tubes, a plurality of spaced tubes extending axially to the space defined within said inner wall, means for passing a third heat transfer medium through said straight tubes, the space within said inner wall and surrounding the spaced tubes therein being open at one end to the atmosphere surrounding the heat-exchanger and being closed at its opposite end and the inlet to said annular space located at and being in communication with the opposite end of the space within said inner wall so that the second heat transfer medium, prior to flowing over said first and second plastic tubes, passes over said spaced tubes in the space within said inner wall so that the second heat transfer medium is preheated in advance of its introduction into said annular space.
 3. A heat-exchanger, as set forth in claim 2, wherein said first means comprises a first annularly shaped end wall extending between said inner wall and said outer wall transversely of the axial direction thereof and forming a closure for one end of said annular space therebetween, and a second annularly shaped end wall connected to and extending radially inwardly from said outer wall transversely of the axial direction of said outer wall at the opposite end thereof from said first end wall and with the adjacent end of said inner wall spaced in the axial direction thereof from said second end wall toward said first end wall so that the space therebetween forms the inlet to said annular space, said second means comprises an outlet member connected to and extending outwardly from said outer wall adjacent said first end wall for forming the outlet from said annular space, said third means comprises a container located radially outwardly from said outer wall relative to said inner wall, an inlet box connected between said container and said outer wall, said first and second tubes extending through said inlet box and connected to said container For receiving hot water from said container for flow through said tubes, an outlet box connected to said outer wall at the opposite end thereof from said inlet box and arranged to receive the outlet ends of said first and second tubes, inlet means connected to said spaced tubes within said inner wall and spaced axially outwardly from said first end wall so that the space within said inner wall is opened at the end adjacent said inlet means, and outlet means connected to said spaced tubes within said inner wall and connected to said second end wall and extending transversely of the axial direction of said inner wall and forming a closure for the end of said space within said inner wall opposite the end located adjacent said inlet means.
 4. A heat-exchanger, as set forth in claim 3, wherein said inner wall and outer wall, said straight tubes, said inlet and outlet means for said tubes, and said container, said inlet box and outlet box associated with said helically wound first and second tubes are all formed of plastic material.
 5. A heat-exchanger, as set forth in claim 3, wherein said container is open to the atmosphere, and a level regulator located within said container for regulating the level of hot water therein for limiting the pressure within said first and second tubes. 